Turbine blades used in gas turbine engines for various industrial, power generation, marine, and transportation applications have a shroud with so-called Z-notches which are configurations in the turbine blade shroud having a “Z” shape. Adjacent blades interlock at the Z-notches. Because these Z-notches are points of contact between adjacent turbine blades, the contact faces of Z-notches experience wear and erosion. It is therefore desirable that these contact faces are surfaced with a material having high temperature wear and erosion resistance. Furthermore, these contact faces require repair and resurfacing from time-to-time.
Turbine blades are generally cast from superalloys having high levels of nickel and/or cobalt. One such alloy is GTD-111 which has a nominal composition, by weight, of 14% Cr, 9.5% Co, 4.9% Ti, 3.8% W, 3% Al, 2.8% Ta, 1.6% Mo, 0.02% Zr, 0.1% C, 0.012% B, and balance Ni. Surfacing, resurfacing, and repairing components made from GTD-111 and other superalloys by welding techniques present serious technical challenges. For example, plasma transfer arc (PTA) welding involves such high direct heat input to the blade surface that it results in partial melting of the blade material. This is problematic if the blade material is directionally solidified material, because the directional characteristics are lost upon cooling. High heat input weld overlay processes can disadvantageously impart a heat-affected zone to the substrate and alter material characteristics near the heat-affected zone, often causing the blade to become embrittled in that region. Thermal spray processes require substantial clean-up which is inefficient and can risk substrate damage, and the resulting bond is primarily mechanical and not as good as a true metallurgical bond. Using pre-sintered preforms requires a separate brazing material and machining of the substrate, resulting in a diffusion zone in the substrate that has a detrimental effect on its properties.